1. Field of the Invention
The present invention generally relates to fingerprint apparatus and fingerprint method using a fingerprint input apparatus capable of directly reading a fingerprint image and, more particularly, to personal identification and security systems and methods using such fingerprint input apparatus.
2. Background Description
In a conventional fingerprint input apparatus, the skin surface of the fingertip is irradiated with light at a predetermined angle using optical components such as a lens and prism or optical fiber. The light reflected by the skin surface is focused to output a fingerprint image. In another conventional fingerprint input apparatus, an apparatus that emits a light toward a portion of a finger other than the finger pad and detects a light emerging from the inside of the finger. The apparatus has a special component between a finger and an image sensor which selectively reflects the light emerging from the finger Alternatively, a scheme of directly inputting a fingerprint image using an electrostatic capacitance instead of obtaining a fingerprint image using the optical system has been proposed.
U.S. Pat. No. 6,414,297 (corresponding to Japanese patent JP 11-259638) to Sasaki, a two-dimensional photo-sensor is provided over a surface light source. The surface light source emits light upwardly to the finger pad. The light reflected by the surface of the finger is detected by the two-dimensional photo-sensor a the semiconductor layer. With the radiation of the light, electron-hole pairs are accumulated in the channel region of the semiconductor layer resulting in a flow of a drain current. The acquired image has bright ridge portions and dark valley portions. A transparent conductive layer is interposed between the two-dimensional photo-sensor and the finger. The transparent conductive layer dissipates static electricity, which may cause a malfunction of the two-dimensional phot-sensor.
U.S. Pat. No. 6,381,347 to Teng discloses an apparatus for detecting the light scattered by the ridge portion of the finger pad by use of a prism, which is provided between a fingerprint and an image sensor. A light emitted from a light source strikes a scattering surface and internally scatters in prism. A relatively large percentage of incident light will strike imaging surface at an angle less than the critical angle. An incident light which strikes a fingerprint valley will substantially pass through the imaging surface. Light striking a fingerprint ridge will substantially scatter and produce a scattering light, which will be detected by an image sensor through a lens assembly 314. The acquired image has bright ridge portions and dark valley portions.
Japanese Patent No. JP 8-180173A to Fujieda discloses an apparatus comprising a flat light source, an edge sensor, and an optical component. The light emitted from the flat light source goes through the image sensor and reaches the optical component. The optical component creates a tilt in the path of the light emitted from the flat light source. The light with a tilt strikes a finger pad and a reflected light is produced. The reflected light reaches an image sensor through the optical component.
Japanese Patent No. JP 1-281583 A to Kato discloses an apparatus detecting a light emerging from the inside of the finger rather than a light reflected by the surface thereof. The apparatus includes a light guide board and LEDs. The LEDs emit light toward side portions of a finger. A portion of the light enters the finger and reaches the interface surface between the finger and the light guide board. A light emerging from the valley portion passes through the light guide board and disappears. A portion of the light emerging from the ridge portion travels inside the light guide board repeating total internal reflections and reaches a detector. The acquired image has bright ridge portions and dark valley portions.
Japanese Patent No. JP 7-171137 A to Tomita discloses an apparatus for detecting a light emerging from the inside of the finger by means of a fiber optical plate (FOP) 1. A light source downwardly irradiates a fingernail side of a finger. The light emerging from the inside of the finger is received by the FOP. The FOP includes a number of optical fibers each of which comprises a core, a clad and an absorbing body. An edge surface of the FOP is shaped to have a slope of an angle θ. The angle θ is carefully selected such that an incident light entering from air in the valley portion does not undergo total internal reflection at the interface between the core and the clad, and would be absorbed by the absorbing body, irrespective of the angle of incidence. Because the finger has an index of reflection different from that of air, a portion of an incident light entering from the ridge portion undergoes a total internal reflection, travels inside the FOP, and then reaches a CCD sensor. The acquired image has bright ridge portions and dark valley portions.
Japanese Patent No. JP 6-300930 A to Shikai discloses an apparatus similar to that of Tomita. The apparatus of Shikai includes lighting means and a bundle of optical fiber. The lighting means emits a light toward the tip of a finger. The bundle of optical fiber has an oblique incident surface. The oblique angle of the incident surface is selected such that a light emerging from the ridge portion travels through the optical fiber and a light emerging from the valley portion does not. The acquired image has bright ridge portions and dark valley portions.
The first category of references discloses an apparatus that emits light toward a finger pad and detects a light reflected from the surface thereof. The Sasaki, Teng and Fujieda references fall into this first category. The second category of references discloses an apparatus that emits a light toward a portion of a finger other than the finger pad and detects a light emerging from the inside of the finger. The Kato, Tomita and Shikai references fall in the second category.
In these conventional fingerprint input apparatuses, when the optical components such as a lens and prism or a fiber are used, a space for the sizes of these optical components and their mounting positions is required to result in a large thickness and size of the apparatus. In addition, since these optical components are relatively expensive, the apparatus cannot be manufactured at low cost. When the fingerprint image is optically processed using these optical components, the resultant image tends to distort.
U.S. Pat. No. 6,016,355 to Dickinson discloses a transparent non-conductive layer provided over a sensor. The apparatus disclosed in the Dickinson reference measures a change in capacitance with respect to the parasitic capacitance caused by an uneven surface of a finger pad. An insulating material such as glass or plastic is disposed above sensing elements as a sensing surface.
U.S. Pat. No. 6,055,324 to Fujieda discloses a fingerprint entry device of the electrostatic capacitance sensing type. The fingerprint entry device has an electrode in the form of mesh or comb for radiating a high frequency wave toward a finger, a plurality of signal sensing electrodes for forming electrostatic capacitance between the electrodes and the finger and a switching means for consecutively connecting each of the signal sensing electrodes to a signal sensing circuit.
The scheme of directly inputting a fingerprint image using electrostatic capacitance is susceptible to external static electricity and difficult to obtain a high sensitivity.
U.S. Pat. No. 6,636,620 to Hoshino discloses a personal identification system for a client terminal in communication with a server. In this system, a client terminal user impresses one's fingerprint on a fingerprint sensor and puts an one's IC card into a card reader. The IC card stores personal information of a card owner, which information includes information related to a fingerprint and an ID number of the card owner. The client terminal includes an authenticator, which provides an authenticating signal if the sensed fingerprint information of the client terminal user matches stored fingerprint information of the card owner. The client terminal transmits the stored personal information of the card owner to the server upon occurrence of the authenticating signal. The server, in turn, transmits an authorizing signal to the client terminal if the transmitted personal information of the card owner matches stored personal information on a server database. Upon receiving the authorizing signal, the client terminal user is authorized to access a computer of the server.